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Deleting a Few LOC Can Yield “Significant” Power Savings on Some Linux Systems
- voltagex_ 6y agoSo what's the cumulative amount of power wasted?
- ggreer 6y agoDepends on the system. On newer Intel machines, it will prevent the SoC from going into lower power states than PC2. On my laptop, that means idling at 5 watts instead of 2ish watts. That said, I don't think any laptop has a PCIe to PCI bridge. This should only affect some desktops and servers.
- jack95 6y agoClickbait title
- MaxBarraclough 6y agoAgree. It would be better if it gave the maximum amount of technical detail possible given the space constraint.
- rbinv 6y agoNot really.
- clarry 6y agoTo save you a click: There was code that disabled ASPM[1] when you have a PCI bridge connected downstream of PCIe. That code is gone now. https://en.wikipedia.org/wiki/Active_State_Power_Management https://en.wikipedia.org/wiki/Active_State_Power_Management
- kees99 6y agoReminds me of the Raspberry pi 4 update, where enabling ASPM shaved something like 10% off the idle power consumption: https://www.cnx-software.com/2019/06/29/new-raspberry-pi-4-vli-firmware-lowers-temperature/ https://www.cnx-software.com/2019/06/29/new-raspberry-pi-4-v...
- segfaultbuserr 6y agoIt's increasingly difficult to do power saving in modern laptops with highly integrated SoC - a single component can prevent the entire system from entering a deeper power saving state. In the old days, CPU and graphics were basically everything, but there can be an endless number of traps today, a SATA driver, an audio driver, or a PCI bridge in this case, not to mention that many subsystems are poorly documented. And even if the potential of power saving in a device driver is identified, it's often plagued with mysterious bugs (the Window driver may include nonstandard workarounds). Only Intel knows everything, I guess even Microsoft doesn't (try running Windows without all the Intel chipset drivers installed...). If you take a modern laptop and put Linux on it, it's possible that you'll only able to get 50% of the battery life. And there's nothing you can do about it.
- throw4839 6y agoAMD is now doing new power saving system basically from scratch. I really hope it will be linux friendly.
- TomMarius 6y agoMy Dell XPS had less than 30% with latest Ubuntu (after powertop) :\
- segfaultbuserr 6y agoI'd say powertop is almost useless today. It was designed in an era when individual devices were loosely-coupled, you could simply identify the power hogs one-by-one and fix them. Today, power management is tightly-coupled with many subtle interactions and dynamic behavior. The most-common failure mode today: something prevents the SoC from entering a deeper sleep mode - you can't fix it with powertop, better to start reverse engineering firmware and Windows drivers... :(
- cesarb 6y agoI'd say powertop can be worse than useless today. Its suggestions are too aggressive, it suggests min_power which can cause data corruption, instead of med_power_with_dipm which is the recommended value nowadays.
- manicdee 6y ago“Old patch disabling Active State Power Management deleted, significant energy savings expected on some ancient hardware.”
- baybal2 6y agoI see this as a flaw of Linux development model, and how code from hardware vendors gets a free go. When Linux was still small, each and every major hardware platform was worked on until mirror polish, and it worked "well." Now, the only criteria, when Linux mainly relies on hardware maker programmers to do their job, is that the code compiles and works. Without much pressure from users, there is nobody to push against "barely works" driver code.
- fred_is_fred 6y agoI don't think this is a specific PCI driver but core to how the PCI subsystem works.